Tag: the p-block elements - group 13

Questions Related to the p-block elements - group 13

The correct statement(s) about orthoboric acids is/are :

chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

  1. It behaves as a weak acid in water due to self ionization.

  2. Acidity of its aqueous solution increases on adding ethyl alcohol.

  3. It has three dimension structure due to H-bonding.

  4. It is a weak electrolyte in water.

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Correct Option: B,D

Which one of the following statements about $H _3BO _3$ is not correct?

chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

  1. It is a strong tribasic acid

  2. It is a prepared by acidifying an aqueous solution of borax

  3. It has a layer structure in which planar $BO _3$ units are joined by hydrogen bonds

  4. It does not act as proton donor as it acts as a Lewis acid by accepting hydroxyl ions

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Correct Option: A
Explanation:

It is weak monoprotic acid and it does not act as proton donor but removes proton from water.

$B _{2}Ca _{6}O _{11}+ Na _{2}CO _{3}\overset{\Delta }{\rightarrow}\left [ X \right ]+CaCO _{3}+NaBO _{2}$ (unbalanced equation)
Correct choice(s) for [X] is/are:

chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

  1. structure of anion of crystalline [X] has one boron atom sp$^{3}$ hybridised and other three boron atoms sp$^{2}$
    hybridised

  2. X with NaOH (aq.) gives a compound which on reaction with hydrogen peroxide in alkaline medium yields
    a compound used as brightner in soaps

  3. hydrolysis of [X] with HCl or H$ _{2}$SO$ _{4}$ yields a compound which on reaction with HF gives fluoroboric acid

  4. [X] on heating with chromium salts in oxidising flame gives green coloured bead in cold

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Correct Option: B,C,D
Explanation:

Compound [X] is Na$ _{2}$B$ _{4}$O$ _{7}$
(A) two boron atoms are $sp^{2}$ while other two boron atoms are $sp^{3}$ hybridised.
(B) product is sodium peroxoborate which is used as brightner in soaps.
(C) $H _{3}BO _{3}$ is formed which with HF gives $HBF _{4}$.
(D) Green bead in oxidising as well as in reducing flame in cold.

Boron can undergo the following reactions with the given enthaly changes:
Assume no other reactions are occurring. If in a container (operating at constant pressure) which is isolated from the surrounding, mixture of are passed over excess of B(s), then calculate the molar ratio so that temperature of the container do not change :
${\text{2B}}\left( {\text{s}} \right){\text{ + }}\dfrac{{\text{3}}}{{\text{2}}}{{\text{O}} _{\text{2}}}\left( {\text{g}} \right) \to {{\text{B}} _{\text{2}}}{{\text{O}} _{\text{3}}}\left( {\text{s}} \right);\;\Delta H =  - 1260\;KJ$
${\text{2B}}\left( {\text{s}} \right){\text{ + 3}}{{\text{H}} _{\text{2}}}\left( {\text{g}} \right) \to {{\text{B}} _2}{H _6}\left( g \right);\;\Delta H = 30KJ$

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. 15 : 3

  2. 42 : 1

  3. 1 : 42

  4. 1 : 84

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Correct Option: C

Moissan boron is:

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. 95 - 98% pure amorphous boron

  2. 75 - 78% pure amorphous boron

  3. 95-98% pure crystalline boron

  4. 75 - 78% pure crystalline boron

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Correct Option: A
Explanation:

Moissan Boron is amorphous Boron of ultra high purity.

For healthy growth of plants, boron is an essential:

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. minor nutrient

  2. major nutrient

  3. both

  4. major metal

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Correct Option: A
Explanation:

Boron is essential for the growth of higher plants. The primary function of the element is to provide structural integrity to the cell wall in plants. 


Other functions likely include the maintenance of the plasma membrane and other metabolic pathways.

So it is essential micronutrient for plants.

Option A is correct.

Which of the following is used as control rods in nuclear reactors?

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. Al

  2. Ga

  3. Tl

  4. B

Show answer
Correct Option: D
Explanation:

Boron carbide is used as a control rod material.

Diborane undergoes cleavage and gives aduct with
(i) CO
(ii) $ H _2O $
(iii) $ N(Me) _3 $
(iv) $ NH _3 $

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. i, ii

  2. i, iii

  3. ii, iii

  4. i, iv

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Correct Option: A

Borazole is an isoster of

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. Benzene

  2. Propane

  3. Naphthalene

  4. Phenol

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Correct Option: A
Explanation:

Both have number of electrons and similar structure and properties.
Isosteres are molecules or ions of similar size containing the same number of atoms and valence electrons, e.g., O^2-, F-, Ne.

Diborane does not react with?

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. $Cl _{2}$

  2. $Br _{2}$

  3. $I _{2}$

  4. all

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Correct Option: C